(1) Field of the Invention
The present invention relates to a polyester composite or laminated film (referred to as a polyester laminated film hereinbelow) which comprises delustered layer(s) and a transparent layer.
More specifically, the present invention relates to a laminated film which has a delustered layer with gloss of less than 15% and more preferably, of less than 10% based on the method of JIS-Z-8741, and transparency with total light or luminous transmission ratio higher than 60% as measured by the method of JIS-K-6714.
It should be particularly noted that the present invention relates to a laminated film superior in transparency, in which the transparency thereof is not reduced despite the fact that its surface is sufficiently roughened.
(2) Description of Prior Art
Conventionally, various kinds of tracing films have been widely employed which are produced by roughening the surface of an oriented polyethylene terephthalate film so as to be superior in writing ability (referred to as writability hereinbelow) and transcribability by pencils, ink, indian ink, etc., and moreover, capable of observing written items, printed matters, etc. placed at the back of said film through the surface thereof.
For example, in U.S. Pat. No. 4,067,855, there is disclosed a biaxially oriented polyester film which contains 0.2 to 3.0% by weight of "reactive particles" consisting of lithium and phosphorus as a lithium salt of phosphoric acid ester constituent of short chain polyesters.
Meanwhile, in Japanese Patent Publication No. 31908/1978, there is also disclosed a delustered polyester film which is produced by uniaxially or biaxially orienting a saturated linear polyester which contains 0.5 to 30% by weight of glass fibers having fiber length shorter than 0.5 mm and fiber length/fiber diameter of larger than 5.
In the known films as described above, however, there have been disadvantages. For example, since it is necessary for the films to contain a large amount of particles in order to increase the surface roughness, the resultant films undesirably become opaque, while films superior in writability and delustering cannot be obtained, if the amount of particles to be contained is excessively small.
Meanwhile, in British Pat. No. 1,096,064, there is also disclosed a laminated film which contains an inert additive in the outermost layer. In the above conventional film, however, there have still been such drawbacks as described hereinbelow.
(1) Even when a large amount of inert particles is added to the outermost layer, the surface undulation or unevenness during stretching is not sufficiently deep, and therefore, favorable delustering effect as in the sand-blast process is not available. PA0 (2) On the contrary, as the amount of addition is increased, the film becomes undesirably cloudy so as to be opaque. PA0 (3) Meanwhile, if the delustered layer is thickened or the amount of addition of inert particles is increased for the improvement of the delustering effect, the stretching ratio is limited by the breakage or tearing during stretching, and thus, films superior in mechanical properties are not available.